Predominantly base metal alloys 11D087(68)-slide no:1-10 11D088(69)-slide no:20-27 11D089(70)-slide no:28-39 11D091(71)-slide no:12-19
Predominantly base metal alloys • Introduction • As the prices of gold increased and mechanical properties were found rather inadequate base metal alloys were tried. • Soon many corrosion resistant alloys of co-cr , co-ni-cr , etc…were introduced into the field.
Definition: • These are mainly base-metal alloys which may or may not contain any noble metals (0-25%).
Characteristics properties • High corrosion resistance • Superior mechanical properties • Low density • High fusion temperature around 1300-1600 • White in colour and shine, like stars(stellites ).
CLASSIFICATION OF PBM CASTING ALLOYS 1.Passivation-oxide film. • Chromic oxide film in co base or Ni based alloys • Titanium oxide film in titanium and its alloys. 2.Compositions • Cobalt based , Co-Cr-W , Co-Cr-Mo , Co-Ni-Cr • Nickel based : Ni-Cr-Mo , Ni-Cr-Be , Ni-T • Titanium ,Ti-Al-V , Ti- Mo- Zr- Sn , Ni-Ti • Aluminium bronzes.
3.Fusion temperatures • Low fusing PBM alloys : solidus temp<1300. • High fusing PBM alloys : solidus temp>1300 . 4.Applications • All metal crown and bridges(F.P.D) • Cast removable partial denture(RPD) frame works • Metal ceramics • Dental implants • Orthopaedic implants : Hip joints bone plates, bars ,screws etc.. • Wrought alloy-orthodontic wires • Dental instruments
ADA specification number 14,these alloys should have • Passivating metal- Cr>20%by weight • Major elements- Co+Ni+Cr>85%by weight.(But other compositions complying toxicities and hyper sensitivity limits are also accepted) • Yield strength>500MPa • Elongation percentage>1.5% • Modulus of elasticity>1,70,000MPa
Cobalt:0-65% • Nickel:0-80% • Co+ Ni=60%-65% • Chromium:15-30% in cobalt based alloys and 11%-17% in Nickel based alloys. • Molybdenum or Tungsten:5-10%-hardeners. • Beryllium:1-2%,decreases M.P • Trace- metals for increasing mechanical properties- Al, Fe, Cu ,W, Mo. • Trace-metals for grain refinements Iridium,Ruthenium. • Trace metals for scavenging-Manganese , Indium • Carbon 0.2%-0.5%-effective hardener ,the types of carbide precipitation control hardness.
ALLOYING PROPERTIES • ALLOYING PROPERTIES 1.Chromium:Medium density=7.15gm/cc , high MP=1875. Increases: Corrosion resistance , by forming Cr₂Ofilm. Yield strength , modulus of elasticity(stiffness)by solution hardening , and M.P. Decreases : Ducility , malleability and elongation at fracture , Cr>30% causes brittleness 2.Cobalt:Medium density=8.85gm/cc , MP=1495. Increases: hardness ,YS , MOE(stiffness),MP, Decreases : Ductility , malleability ,elongation at fracture.
3.Nickel:Medium density=8.9gm/cc , MP=1453 . Increases: hardening,YS ,M.O.E and M.P to less extent. Decreases :ductility ,malleability ,and % elongation to less extent. 4.Mo or W:increaseshardness ,YS and MOE .But Mo doesn’t decrease ductility and percentage elongation as W. 5.Berilium:increases strength but decreases melting point and grain size .Inhalation of toxic vapour or dust in factory , and laboratories cause health hazards-dermatitis etc…
6.Sn ,Al , Cu, W, Mo : Trace elements increase hardness-( Ni₃ Al - phase precipitations). 7.Iridium, Ruthenium,(traces)grain refiners and hardeners. 8.Mn,Zn,Si :Traces scavengers. 9.Carbon : 0.2-0.5% traces-effective hardener , respond to heat treatments.
GENERAL PROPERTIES OF PBM CASTING ALLOYS 1. These have high corrosion resistance due to passivation effect of Cr₂O₃ surface film. 2. Ni and Be are said to be toxic.Inhalation of vapours or dust of these metals cause health hazards.Ni vapours inhalation is found to be carcinogenic and Be vapours cause dermatitis,chest pain etc.. 3. Ni containing alloys have slightly lower, melting temperature(easier to melt)stiffness or modulus of elasticity,YS,UTS,hardness but higher elongation at fracture.
4. Many of these alloys respond to heat treatments,usually by age hardening,annealing and homogenisation etc. 5. All PBM alloys are white in colours(stellites). 6. Trade names:Co-Cr alloys:Vittalium,Genesis,Novarex,Ultra100 Ni-Cr alloys:Ticonium,Resillium111,Neptune,Lite cast Co-Ni-Cr alloys:Nobillium. Gold alloys :Jelenko,orion,Deva 4,Jelenko-SMG-3 Dequdent,Cameo.
CLINICAL ASPECTS • 1.Clasp adjustments: modulus of elasticity(stiffness)of PBM alloys(200,000MPa) are nearly double that of HN or N alloys.The force to be applied for clasp adjustment is hence nearly double.Also since double force is required to dislodge the clasp,tooth preparation with lesser under cuts is sufficient.The advantage is less removal of tooth material.
2.PBM alloys undergo work hardening more easily which reduces its life time. • 3.Even though PBM alloys are cheaper,the auxillary materials (like phosphate bonded investments,special casting equipments,skilled technicians with intensive training,time consuming procedure,sophiscated laboratories (with sand-blasting , electropolishing etc… equipments)make the appliance quite expensive.
MICRO STRUCTURE-METALLOGRAPHY OF PBM ALLOYS During solidification,dendritic structured grains of the various solid solutions phases of different components are formed in different,directions forming grain boundaries. Co-Cr,Moform eutectic alloys at1275 and precipitate as lamellar structures.All these increase slip resistances or hardness.Carbon can combine with all these component metals forming their carbides.These carbides have fusion temp lower than other solid solutions. Hence the liquid carbides solidify last, in the inter –dendritic space and at the grain boundaries.
These carbide precipitation increases hardness and decreases ductility,depending on the nature and site of precipitation such as, • Continous thin dark layers or lines, at grain boundaries if casting is done as soon as solid alloy is melted.This increases brittleness,decreases elongation percentage,but produce smooth casting suface.
Lamellar eutectoid type structures of different phases, are formed on slow cooling .But increases brittleness. • Sperical island like structure in between the grains,if the alloy liquid is heated to 100above its liquidus before casting.It has very poorsurface quality ,but higher ductility and is not usually done.
Outline of casting procedure of high fusing PBM alloys 1.Master cast and duplicates : Dentist prepares the teeth,to receive the fabrication of required design obtains an accurate impression ,prepares the stone master cast and sends to the laboratory, 2.Performed smooth casting wax patterns are used for designing the partial denture frame works on this duplicate casts.
3.Investment or die material : Colloidal silica liquid is added in required proportions to avail higher setting and thermal expansions for compressive of large casting shrinkage of 2.2 to 2.3% 4.Wax- burn out is done in an electric furnace by slowly raising the temp first upto 300and then quickly about 750 to 850maintained for about 2 hours for completing thermal expansion and wax elimination.
5.Melting of the alloys : Type 1 low fusing PBM alloys of Ni-Cr , having melting temp 110 to 1300and higher fusing alloys of Co-Cr .
Recovery and finishing Final Polishing is done by electro polishing method that is suspending the article as anode in sulphuric acid solution bath and passing direct current for sometime.
CAD –CAM DENTISTRY CAD/CAM dentistry (Computer aided design and Computer aided Manufacturing) is an area of dentistry relitizing CAD CAM technologies to produce different types of dental restorations ,including crowns,crownlays,veneers,inlays and onlays,fixed bridges ,dental implants restorations and orthodontic appliances.
PROCESS Dental restorations are miled from solid blocks of ceramic or composite resins A digital impression is taken draws data into a computer by a dentist Proprietary software is used to create a replacement part for the defect is carved out solid block of ceramic or composite resin
resulting restoration can then be adjusted in the patients mouth cemented or bonded to place
NOTE If CAD CAM restorative materials is Zerconium-Oxide or Lithuim –Disilicate ,the restoration will become radio-opaque just as metal restorations are,that is these materials block x-rays.
USES • Dental laboratory industry • Providing for dental fabrication of dental prosthesis • Raging from orthodontics appliances to dental implants and crowns to long span fixed bridges.
DISADVANTAGES • The accuracy of crowns and bridges using this technology is not as consistent as some other dental fabricating process • This is because crowns and bridges require extremely precise fits in teeth abutments or steps that require dentist hand.
List of CAD CAM dental software products • CEREC : software for manufacturing crown ,veneers , onlays , inlays can be prepared using different types of ceramic material • Decam dental solutions :for the design and manufacturing of capings and bridge frameworks. • Work NC dental from Sescol , CAD CAM for automatic machining of prosthetic appliances, implants, bridges or dental structures